Method for inhibiting current harmonics based on FFT (Fast Fourier Transform)

A technology of Fourier transform and current suppression, applied in AC network to reduce harmonic/ripple, harmonic reducing device, measuring current/voltage, etc., can solve the problem of large error, inability to obtain harmonic amplitude and phase information, design Difficulty and other issues

Inactive Publication Date: 2016-07-13

LEIHUA ELECTRONICS TECH RES INST AVIATION IND OF CHINA

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AI-Extracted Technical Summary

Problems solved by technology

The center frequency of the analog filter detection method is very sensitive to the component parameters, etc., the design is difficult, and the error is large; the detection method based on the inst...

Abstract

The invention belongs to the technical field of power grid harmonic detection, and relates to a method for inhibiting current harmonics based on FFT (Fast Fourier Transform). According to the technical scheme of the invention, the method can extract any harmonic and the sum of harmonic components meeting conditions. When a load harmonic current exceeds the compensation capacity of an APF, the method can select the characteristic harmonics with the bigger dangers to be compensated. The method can carry out IFFT of the harmonics meeting the conditions, and then extracts the sum of a part of harmonic components, so that the APF just compensates the needed harmonics in an occasion where the method is used cooperatively with a passive filter.

Application Domain

Current/voltage measurementHarmonic reduction arrangement +1

Technology Topic

PhysicsFft fast fourier transform +4

Image

Examples

Experimental program(1)

Example Embodiment

[0020] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0021] In response to the requirement of extracting the sum of harmonic components that meet the conditions, the present invention proposes a fast Fourier transform-based aircraft AC power harmonic detection method, but it is not a limitation of the present invention, and the embodiment is only To illustrate the principle of the present invention, there will be various improvements to the present invention, and these improvements fall within the protection scope of the present invention. This example illustrates its implementation process through Matlab simulation software.

[0022] (1) Refer to the typical waveform of load current of the rectifier circuit figure 2;

[0023] (2) The AC power frequency is f=400Hz;

[0024] (3) Determine the frequency f at which the A/D converter of the DSP processor samples the load current s =50kHz;

[0025] (4) Number of sampling points in a period

[0026] (5) Take the FFT data operation length N=2 8 =128;

[0027] (6) The CAP unit detects the edge of the square wave signal;

[0028] (7) Start the software to perform N=128 FFT transformation on 125 sampled discrete data sequences to obtain discrete complex number sequences X[1], X[2]...X[128];

[0029] (8) Calculate the power spectral line amplitude of the complex number sequence A[1], A[2]...A[128];

[0030] (9) Search the amplitude, perform inverse FFT transformation on the spectrum whose power spectral line amplitude is less than A[2]=8217.3; obtain the sum of harmonic components;

[0031] (10) The result of the sum command of the harmonic components and the actual compensation current passing through the proportional-integral regulator, through the digital signal processor PWM module triangular wave modulation, generates the compensation circuit drive signal, and completes the harmonic compensation;

[0032] (12) Refer to the power supply current waveform after compensation Figure 4 , The power current waveform is more sinusoidal, and the harmonic content is lower than the load current.

[0033] (13) Search for the amplitude, and perform inverse Fourier transform (IFFT) on the spectrum whose power spectral line amplitude is less than A[3]=1677.9; to obtain the sum of harmonic components, see Figure 5;

[0034] (14) The result of the sum command of the harmonic components and the actual compensation current after passing through the proportional-integral regulator, through the digital signal processor PWM module triangular wave modulation, generates the compensation circuit drive signal, and completes the harmonic compensation;

[0035] (15) Refer to the power supply current waveform after compensation Image 6 , The power current waveform is more sinusoidal, and the harmonic content is lower than the load current.

PUM

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